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Fostering the Remediation & Redevelopment of
Manufactured Gas Plant Sites

Jeff Gentry


Presentation Title

Selection of In-Situ Stabilization Areas for NAPL-Impacted Sediment Remediation and Treatment Cap Design  

Jeff Gentry, Principle Technologist, Jacobs 

Co-Authors: Paige Molzahn and Juliana Hess, Jacobs


Background/Objectives. In 2013, EPA issued a Record of Decision (ROD) for cleanup of the canal, which specifies a multicomponent sediment remedy that includes: 1) dredging of the soft sediment, 2) in-situ stabilization (ISS) of native sediments in areas of the canal with the potential for upward NAPL migration, and 3) capping the entire canal with a multilayer cap system. Selection of the areas targeted for ISS is a critical step in the remedial design (RD) and the implementation of the ROD requirements.  Areas if ISS affect groundwater discharge which effects the depth of the treatment layers needed for the cap.

Approach/Activities.The in-situ characterization included analysis of several TarGOST borings located throughout the canal. Laboratory analyses specific to NAPL migration and mobility included evaluation of pore fluid saturation, NAPL mobility testing by water drive, NAPL mobility testing by centrifuge, and controlled gradient mobility tests. Finally, sediment cores were analyzed using laser induced fluorescence frozen core analysis which was matched to the TarGOST RE response for each sediment.

This large data set was analyzed and the results were presented to the EPA. Of the 67 TarGOST sample locations in the upper canal, 40 had a threshold exceedance for saturation based in the TarGOST correlation. After the analysis presented in this presentation was performed, EPA issued a directive to the PRPs to include 26 locations for ISS in the RD for the upper canal.

The areas of ISS were then incorporated into the groundwater model to analyze the effect of specific discharge and contaminant migration. Groundwater specific discharge into the canal was also affected by the removal of soft sediment also required by the ROD.  EPA used an approach where the post remediation groundwater discharge should not be significantly altered because of concerns about neighborhood flooding.  A final configuration of ISS areas and the associated treatment cap layer thickness has been developed to the 90 percent design level and will be shown in this presentation. 


Principle Technologist for the investigation and remediation of sediment with Non-Aqueous Phase Liquid (NAPL) impacts.  Session chair for 2019 Battelle Sediment conference on NAPL sites.  Since 2012, senior advisor to EPA for the Gowanus Canal.  Supports EPA on the Wyckoff Superfund site with nearly 5 acres of NAPL impacts in the intertidal area.  Supports private clients mostly in California and the Pacific Northwest, notably for Kinder Morgan to implement an innovative sheen control technology on the shoreline of the Portland Harbor Superfund Site.